It is known by manufactures and users of grain and seed dryers that the following drying methods (with respect to intermittency) are currently available to the industry:
a) Intermittent dryers (equipped with a holding chamber): commonly used for seed drying, as the overall drying process is less aggressive but slower, therefore not suitable for large-scale grain drying. In these dryers, a pulsating flow of hot air dries the product until the desired moisture is reached. This process provides effective use of thermal energy for air heating (energy efficient), mostly because of a holding chamber that accommodates small batches of grain at a time as they gradually dry, which significantly reduces its potential aggressiveness during the process. However, for faster drying rates (and the demand for faster drying has increased in the last few years), the drying air needs to be warmer, which may jeopardize the quality of the seeds. Batch drying methods are considered non-efficient because lengthy periods of time are required between product loading and unloading (usually 20 to 40% of effective drying time).
b) Uninterrupted drying: a continuous flow dryer, fed by heated air, is loaded with humid product that remains inside for a predetermined period of time until it is completely dried out and ready for uninterrupted unloading and subsequent processes. Cross-flow (column or rack), mixed, or concurrent flow dryers are included in this category. They may or may not be equipped with a cooling system, which is dependent upon the availability of cooling devices in the dying site. These dryers are generally used for grains and require large air flow intake in order to maximize drying time. They are very aggressive to the grain, causing cracks, quality loss, and major damage to the entire chain. Energy efficiency is very low and in some cases, 60% of energy is wasted during the process.
Brazilian patent MU8602084—Improvements Introduced to Grain Drying Devices. The utility model presented therein consists of a constructive structure that employs vertical towers and an external closure system, intended for static, intermittent, and continuous grain drying process, starting from the loading of product that has been already homogenized and moisture elimination through an exhaust system, interspersed with drying and internal air cooling/heating control mechanisms.
Brazilian patent PI0403421—Grain, Batch, Intermittent, and Concurrent Flow Dryers for Drying; and Counterflow Dryer for Cooling, with Suction System or Air Inflation. The operational features designed for that system provide uniform drying, requiring specific low enthalpy without causing grain damage due to thermal stress, still preserving its original properties. The technical features are commercially suitable for coffee and rice drying, or any other type of grain. It is also suitable for agriculture applications, where pre-processing units provide high drying capacity.
U.S. Pat. No. 6,223,451—Apparatus for drying granular objects involving pre-heating process. An apparatus for drying granular objects described therein has, from the top of the apparatus, a holding section; a heating section for heating the granular objects flowing down from the holding section, the heating section being provided beneath the holding section and having a plurality of air ducts to which heated air is introduced; a drying air producing section connected to the air ducts, in which the heated air from the air ducts is mixed with air taken-in from the outside of the apparatus to produce a drying air; and a drying section for drying the granular objects by directly exposing the granular objects to the drying air. The dried granular objects are taken out from a taking-out section and returned to the holding section through a bucket elevator. The apparatus further has a detector for detecting the temperature of the drying air. Based on the detected temperature, a control device controls the temperature of the heated air so as to keep the temperature of the drying air to a predetermined temperature. The temperature of the drying air can be set to a desirable temperature while the heated air for the heating is kept at a high temperature. The drying operation is performed speedily and safely.
U.S. Pat. No. 4,486,960—Modular drier for drying grains. A modular drier is described therein. Each module has two fans each supplying a common diffusion chamber disposed between two columns of a group of columns. Said chambers adjoin a perforated wall of said columns comprising vertical deflectors, with the opposite wall of these columns, likewise perforated, communicating with a common chamber for exhausting the air used for drying. The technology relates to a modular drier for drying grains, in which gravity draws the grain down in parallel sheets within vertical columns crossed horizontally by the drying air.
Chinese patent CN101738074—Combined Grain Drying Machine. A combined grain drying machine is described therein. The drying machine has a lower body, a lower drying part, a lower storage part, an upper drying part, an upper storage part, an upper auger, a grain inlet elevator, a dust discharging fan, a right air passage, a loading hopper, a lower auger, a grain cleaning valve, a grain discharging elevator, a left air passage, a grain discharging pipe and the like. The drying machine is characterized in that: each of a drying machine body and the air passages adopts a building-block combined structure; the drying machine is provided with a plurality of drying sections; and each drying section comprises a storage part and a drying part. The drying machine introduces a heat medium at an appropriate temperature from a left rear part through an air inlet passage and discharges dried damp air from a right rear part through a centrifugal fan and an air outlet passage. The left air passage and the right air passage are arranged among the drying sections of the drying machine; and each of the left air passage and the right air passage comprises an upper air chamber, an upper cover plate, a lower air chamber, a lower cover plate and a vertical air pipe. The vertical pipes are connected with the upper air chamber and the lower air chamber through trilateral flanges, and are connected with each other through a quadrilateral flange. Application shows that the drying machine adopting the combined structure is convenient to manufacture, transport, assemble and disassemble and dried grains have uniform water content and high quality.